There is a lot of confusion surrounding the distinction between Search Engine Optimization (SEO) and Search Engine Marketing (SEM). SEO is characterized by organic website optimization, while SEM usually refers to paid advertising like Pay-Per-Click (PPC).
SEO is an organic growth that can take months to mature and bear fruit but rewards you with a higher overall baseline. This article
by Josh Steimle does a great job of illustrating the typical process and timetable that can be expected for SEO to show significant results.